Any scratches, scuffs, knocks, cracks or other issues I should be aware of?

There are a reasonable amount of scuffs and very faint scratches on the back, although nothing that affects the iPod's performance or makes it too unnatractive (if you keep it in any of the cases then you'll never even see the back.)

No cracks or dents or anything like that, and the main front screen has had a protector on since day one.